What are some conferences for publishing papers on graph convolutional networks?
Based on past publications, here are some journals and conferences where you can possibly publish or present a research paper on geometric deep learning or graph neural networks


Neural Information Processing Systems (NIPS)
International Conference on Learning Representations (ICLR)
Conference on Computer Vision and Pattern Recognition (CVPR)
International Conference on Machine Learning (ICML)


The website http://geometricdeeplearning.com/ also provides some information about the topic and links you to several workshops, papers, and tutorials. 

Here are some links to some of the past workshops on GDL. 


Representation Learning on Graphs and Manifolds (and the related homepage)
Workshop IV: Deep Geometric Learning of Big Data and Applications
Geometric Deep Learning on Graphs and Manifolds.